Bulk containers of the kind as herein referred are generally made of a fabric material of such an adequate strength that when these containers which are usually filled with a load in the range of at least one ton are handled and subjected to impulsive forces by the lifting means used such as a crane or a fork lift truck no unpredicted failure of the container will occur. For allowing the handling of such heavy loads these bulk containers are usually provided with four lifting loops of such a size as to be engageable over the hook of a crane or the forks of a fork lift truck.
In German Utility Model No. 78 30 440 a prior art bulk container is described as comprising a side wall that is formed with a single, substantially rectangular cut-up of a high tenacity synthetic fibre woven fabric which is double stitched together along two cut edges extending in the direction either of the warp threads or of the weft threads of the material. This double stitch seam which accordingly forms an interconnection seam for the single cut-up of the woven fabric affects the safety factor in respect to the so-called bursting pressure of a fully loaded container so that the side wall structure of this known bulk container is provided with four additional double stitch seams forming four corner seams that accordingly subdivide the side wall structure of the container into two pairs of oppositely parallel wall portions whereby said interconnecting seam is arranged in the middle of one of these wall portions. Each of the corner seams further secures the two legs of a coordinated U-shaped lifting loop to the side wall structure to which opposite of the lifting loops a separate bottom is stitched. With this known bulk container the four corner seams provide a safety factor in respect to the bursting pressure that with a dropping test from a dropping height of 120 centimeter the container when being filled with a load of about 1250 kilograms will not be damaged.
Another prior art bulk container is described in German Utility Model No. 83 31 441.5 as comprising also a single cut-up of a woven fabric for forming its side wall structure with the provision of an interconnection seam for two of its cut edges which instead of being double stitched is being zigzag-stitched by means of a single needle sewing machine. This zigzag-stitched seam provides a safety factor in respect to the bursting pressure of such a value that with this also known bulk container no additional corner seams are needed for obtaining an overall strength corresponding to the strength of a container the side wall structure of which comprises a portion length of a seamless round material as woven at the same time with more tightly packed threads of a comparable superior strength. This kind of a container which further is also provided with a separate bottom as stitched to the side wall structure by means of an oversew stitch and also with four U-shaped lifting loops which through their legs are each secured to the side wall structure by means of additional zigzag-stitches of a short length together with a small cutup of the same fabric may therefore be produced with less costs than all others so far known bulk containers of the same kind.
This invention deals with the object of providing a bulk container of the general kind as above referred which in comparison with the so far known embodiments provides at least the same factor of safety in respect to the bursting pressure under comparable conditions for said dropping test and in addition provides an improved factor of safety in respect to the forces which mainly in a vertical direction are acting on the side wall structure when these bulk containers by means of their lifting loops are engaged over the hook of a crane or the forks of a fork lift truck for their filling and transportation when loaded with bulk material.